As a wave absorber, there have been conventionally known a pyramid wave absorber wherein an urethane foam is impregnated with a conducting material such as carbon, a single-layer wave absorber consisting of a magnetic material whose complex magnetic permeability shows frequency dispersion, such as ferrite, and a composite wave absorber comprising the above-mentioned pyramid wave absorber and the single-layer wave absorber in combination.
In addition, there has been known a wave absorber made of a mat fiber assembly comprising a conductive paint adhered to fibers (hereinafter referred to as mat wave absorber), such as the one applied to a transmitting antenna, for example, at the edge of a parabolic reflector of a parabola transmitting antenna, to prevent interference of a parabola antenna located near.
However, a thin wave absorber such as the aforesaid single-layer wave absorber absorbs only the waves of a narrow frequency range such as from 30 MHz to 400 MHz. On the other hand, a mat type absorber has a drawback that the lower limit of the frequency of the absorbable waves is as high as several thousand MHz, and a wave having a lower frequency than said frequency, for example, 30 MHz cannot be absorbed. In addition, a pyramid or a pyramid.cndot.single-layer composite wave absorber capable of absorbing waves over a wide range of frequencies and having a considerable thickness can result in high production cost and reduction of the effective space in an anechoic chamber where the absorber is set.